The advent and evolution in recent years of technologies and standards for high-rate transmission of packet data over cellular radio access networks has been part of a larger picture that includes advances in the development of packet transport networks and service networks for delivery of packet-data services, all collectively referred to as “third generation” (3G) networks. In the context of the larger picture, there have been industry-wide efforts to coordinate various elemental functions and subsystems within a common architectural framework and based upon common, standard interfaces and protocols for communication. Industry consortia including the 3rd Generation Partnership Project (3GPP) and the 3GPP2, among others, have developed and published specifications relating to numerous aspects of 3G networks, from access devices, to access networks, to core transport networks, to service-delivery networks, as well as the communication methods that form the basis for network operation and services.
Packet-data transport and services in 3G networks are based in a large part on the “Internet Protocol” (IP) and the IP suite of protocol standards. As such, 3G networks themselves incorporate IP networks. In particular, IP-packet-based media services, such as “Voice over IP” (VoIP), video streaming, and packet-media broadcast collectively comprise an “IP Multimedia Subsystem” (IMS) network within a 3G system. Built upon standard signaling protocols, such as Session Initiation Protocol (SIP), standard media transport protocols, such as Real-time Transport Protocol (RTP), and standard policy management protocols such as Common Open Policy Service (COPS), among others, the IMS network provides an infrastructure for integrating new and emerging IP-based services for subscribers in 3G networks. In turn, owners and operators of 3G networks can generate revenue by charging subscribers for IMS-based services according to one or more fee structures, for example.
Within the IMS network, services and applications are usually implemented on one or more servers or application platforms. A subscriber (or user) in a service provider's network accesses communication services via an access terminal (“AT”), such as a cellular or wireless telephone, pager, or appropriately equipped wireless or wireline portable computer, for instance. A user will typically first register with one or more services or applications via the access terminal prior to using the services. More specifically, an AT will execute a software program referred to as a “user agent” (or “UA”) that acts on behalf of the user of the AT in order to, among other functions, register with and invoke the one or more services. In order to simplify the registration process, as well as improve efficiency by reducing registration-related traffic, the IMS network includes a functional element that receives registration requests on a “front end” from users and routes those requests to the appropriate services on the “back end.” In the IMS network, this functional element is called a “Call Session Control Function” (“CSCF”), or more precisely, a “Serving” CSCF (or “S-CSCF”), as described below. A given UA's registration requests may thus be channeled to the proper server or application platform via the S-CSCF, alleviating the need for the UA to directly and separately register with each service.